LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1228 AM CDT Sun May 21 2023
Valid 211200Z - 221200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
INTERIOR NORTHWEST INTO WESTERN MONTANA...
...SUMMARY...
Severe thunderstorms are possible across portions of the interior
northwest into western Montana. Large hail and isolated damaging
gusts will be possible with these storms.
...Eastern WA/OR to western MT...
Upper high, currently centered over western NV, will weaken and sag
south Sunday as a pronounced trough approaches the WA/OR Coast.
Latest model guidance suggests 60-90m 12hr 500mb height falls will
spread across WA/OR into the northern Rockies region late in the
period. Leading edge of large-scale ascent should spread into the
northern inter-mountain region by late afternoon as high-level
diffluent flow aloft increases as far east as western MT.
Pre-trough boundary-layer heating is expected to contribute to
modest instability by mid afternoon as surface temperatures warm
through the 70s at lower elevations. With cooling mid-level
temperatures, lapse rates will steepen significantly and
isolated-scattered thunderstorms should develop ahead of the surging
cold front, initially across southeast BC into northeast WA by 21z,
then farther south into eastern OR by 23z. Forecast soundings
suggest ample surface-6km shear for organized rotating updrafts, and
isolated supercells are probable, along with a mixed mode of
multi-cells and a few clusters. Large hail is expected with the
strongest updrafts and gusty winds may also accompany some of this
activity. Convection should spread east-northeast toward western MT,
by late evening, in advance of the progressive mid-level trough.
..Darrow/Thornton.. 05/21/2023
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